A. Solid Sugars In General
Many solids exist in both crystalline and amorphous forms. Crystals are characterized by an orderly three-dimensional arrangement of molecules in a lattice whereas amorphous solids are characterized by a random arrangement of molecules. The physical properties of the solid often differ markedly depending upon how the molecules are arranged. For example, the physical properties of the element carbon in its amorphous state (e.g., charcoal and coal) and in either of its two crystalline forms (graphite and diamond) are considerably different. It is common for solids to include both crystalline and amorphous formations within the same particle. As used herein, the term "crystalline" refers to a solid having essentially no amorphous formations, the terms "non-crystalline" and "amorphous" refer to a solid having very minor (less than about 10 weight percent) amounts of crystalline formations, and the term "semi-crystalline" refers to a solid having both crystalline and amorphous formations.
Most sugars, including sucrose, glucose (also called dextrose), and fructose, exist in both crystalline and amorphous forms. Crystalline sugars (e.g., common table sucrose) are generally free-flowing granules whereas amorphous sugars tend to agglomerate into a sticky and viscous mass. Therefore, the crystalline form of a sugar is desired for its improved physical properties. Unfortunately, the most common process for producing crystalline sugars, aqueous crystallization, is relatively slow and costly.
The starting point for any crystallization is to obtain a supersaturated solution of the solute to be crystallized in an appropriate solvent. The supersaturated solution is generally achieved by cooling and/or evaporating an unsaturated solution. Although it is an oversimplification, supersaturated solutions are commonly referred to as either metastable or unstable (also called labile) to characterize their behavior. For example, at 20.degree. C., a saturated solution of sucrose in water contains about 2.0 grams sucrose per gram water. If this saturated solution is then cooled and/or evaporated, it initially enters the metastable phase. In the metastable phase, spontaneous crystallization is improbable, but will occur if seed crystals are introduced. If cooling and/or evaporating is continued, the unstable phase is eventually reached and spontaneous crystallization occurs. Most commercial operations induce crystallization in the metastable phase by seeding the solution with previously-formed crystals.
Despite the fact that cooling and/or evaporating aqueous crystallization is slow and costly, it is the major commercial process for producing solid sucrose and glucose. Nevertheless, various processes for producing sugars in semi-crystalline or non-crystalline form have been disclosed. These processes are generally simpler, faster, and less expensive than the conventional crystallization technique because: (1) long crystallization cycles are avoided; (2) the particle size of the product can be determined by mechanical means independently of crystal size; (3) cooling is often eliminated; and (4) the entire product is often recovered without recycle. Therefore, sugars produced by these processes are sold at lower prices than their crystalline counterparts.